Answer: Find the surface area with the formula 
Step-by-step explanation:
<u><em> Since you did not provide the figure, I will give you a general explanation about how to solve this exercise.</em></u>
By definition, the surface area of a rectangular prism can be calculated with the formula shown below:

Where "SA" is the surface area of the rectangular prism, "w" is the width of the rectangular prism, "l" is the length and "h" is the height of the rectangular prism.
Therefore, if you know the length, the width and the height of the rectangular prism, you can follow these steps in order to calculate how much glass was used to make the tank. The procedure is:
Step 1: You must substitute the values of "l", "w" and "h" into the formula.
Step 2: Finally, you must evaluate in order to get the surface area of the rectangular prism (This value is the amount of square inches that was used to make the tank).
Given:
Size of a red blood cell = 0.000007 m
Size of a plant cell = 0.0000127 m
To find:
The comparison of these two values.
Solution:
We have,
Size of a red blood cell = 0.000007 m
Size of a plant cell = 0.0000127 m
Clearly,
. Now, the difference between these two values is:

Therefore, the size of a plant cell is 0.0000057 m more than the size of a red blood cell.
So you have 20% of blue and 50% of black.
So you have 70% in total that are both blue and black.
100%- 70%= 30%
So that means 30% were neither blue or black.
Do a proportion
30/100= x/30
30 x 30= 900
900 divided by 100= 9
Answer is 9 shirts are neither blue or black